The present invention relates to contact irradiation treatment of malignant tumors by laser energy, and more particularly to interstitial applications deeply inside the body of a subject.
Non-contact treatment of surface tumors by laser irradiation has become an accepted medical technique for coagulation, necrosis, and palliation of esophageal, bronchial, colorectal and bladder tumors.
Medical researchers are now seriously considering laser techniques for treating deep seated tumors in the liver, pancreas, prostate, and even in the brain. Interstitial techniques of local hyperthermia deep inside the body offers a safe and sometimes the only effective way of treating such tumors. These techniques can be minimally invasive surgically, requiring only a tiny stab incision, dramatically improving patient comfort and chances of survival and reducing convalescence and recovery time in treatment involving the liver for instance.
An apparatus and method for locally generating hyperthermia-induced coagulation necrosis in tissue masses located deeply within the body are described in applicant's co-pending U.S. patent application Ser. No. 07/534,931, filed Jun. 8, 1990 for "APPARATUS AND METHOD FOR INTERSTITIAL LASER THERAPY". As described in that application, low power laser radiation is introduced into the target tissue mass using an optical fiber extending through a cannula which has been inserted directly into the tissue mass. By activating the laser only during withdrawal movement of the cannula and maintaining a small fluid bolus at the fiber tip, effective and reproducible coagulation of tumor tissue is attained without charring or melting of the probe.
One problem in carrying out interstitial hyperthermia is controlling the temperature of the tissue while it is being irradiated. Hyperthermia destroys both tumor tissue and normal tissue. Laser energy delivered by optical fibers inserted directly into tissue provides an excellent form of local hyperthermia for deep seated tumors of clinical importance (in the liver and pancreas, for example). For this to be of maximum effect, treatment parameters required to destroy all the tumor must be known, namely size of the tumor, laser power and exposure time, and number and location of treatment points. There should be minimal damage to adjacent normal tissue, and subsequent healing of all treated areas, so that acceptable function and mechanical structure of the organ is maintained.
While heating alone, at a sufficient elevated temperature and for a sufficient time, is known to destroy tumor tissue, there is considerable experimental and clinical evidence of additional advantages from interaction between Nd:YAG laser radiation and cancer cells. This is believed to be caused by the direct absorption of laser light by the cancer cells. This is reported in Lasers in Surgery and Medicine Volume 8, Pages 254-258 (1988) in an article entitled "LASERTHERMIA: A New Computer-Controlled Contact Nd:YAG System for Interstitial Local Hyperthermia".
Thus, there appears to be some cumulative advantage in providing the heat energy needed to kill cancer cells through laser light radiated directly into the cells. Further, the laser of preference is stated to be Nd:YAG in the belief that it penetrates tissue deeper than other types of medical lasers.
Temperature distribution through tissue varies, depending on the color of the organ, the rate of blood flow through the organ, and the level of energy applied. In the "LASERTHERMIA . . . " article cited above, a thermogram comparison made in heat conductivity studies on spleen tissue showed the tissue temperature ranged from 50.degree. C. at the heat source to 43.degree. C. six millimeters away, with laser energy input of approximately 5 watts.
Recognizing the importance of keeping the tissue temperature high enough to destroy cancer cells, some prior medical researchers have implanted thermocouples in the tissue to be treated. In applicant's copending application Ser. No. 07/534,931, separate, parallel needles are glued together, 3 mm. apart. One carries an optical fiber and the other carries a temperature-sensing thermocouple. While this is useful as a research tool, it would have serious disadvantages in the real world of practical medical treatment.
In the example mentioned above where the implanted thermocouples were stationary, they could be used only with stationary laser probes because movement of the probes would make the temperature readings meaningless.
Even in the case of the double needle embodiment disclosed in applicant's copending application, it would be very difficult to precisely control the spacing between the thermocouple and the laser tip, especially with long probes. Further, it would require multiple stab incisions or a relatively large incision.